1. Field of the Invention
This invention relates to a household appliance having rotating or reciprocating heads, such as a rotating or reciprocating cleaning brush, electric toothbrush, massager, or polisher.
2. Description of Related Art
The household appliances with which the present invention is concerned normally consist of a head or tool attached to directly to a shaft so as to rotate or oscillate therewith, in order to provide some sort of cleaning, brushing, polishing, or massaging effect.
While it would appear to be difficult to improve upon the brushing, cleaning, polishing, or massaging effect of these conventional household appliances, the inventor has discovered several disadvantages which are solved by the present invention. The disadvantages are 1.) that any rotating device which is pressed against a surface to carry out its function will generate a counter-torque which increases with the power of the device, making the device difficult to handle, 2.) when the surface is uneven, for example at a corner, the device will move erratically due to the lack of symmetry in the motion of the device, 3.) in the case of a cleaning device, debris loosened by the cleaning device will tend to be pressed into the surface rather than removed, and 4.) in the case of a brush having relative long bristles arranged to extend into holes or crevices, for example if the bristles are longer than the circumference diameter of the outer ring of bristles, the bristles will tend to twist in one direction reducing the contact area of the bristles against surfaces of the hole or crevice, as shown in FIG. 21.
The present invention is intended to increase the efficiency of such devices, by splitting the head or tool by which the function of the device is carried out into multiple heads or tools having a differential motion. This has the advantages of 1.) offsetting or canceling out the counter-torque effect, thereby making the device easier to handle,2.) generally balancing the forces applied by the device to permit the device to be used on uneven surfaces, edges, and corners, 3.) providing a cross-cleaning effect at the point where the different sections of the device move in different directions or at different speeds, and reducing bristle twisting effect in the case of a brush.
The solution to the problem of counter-torque in a multiple head or tool device depends, as those skilled in the art might expect once the concept of multiple rotating heads or tools is understood, on the masses and angular velocities of the rotating heads or tools, with the counter-torque being minimized if the masses and velocities are such that the vector sum of the contributions from each of the individual heads or tools to the overall or net torque is zero. In addition, however, the inventor has found that the contact areas and materials of the contact surfaces of the various heads or tools, which contribute to the dynamic friction coefficients of the contact surfaces, also contribute significantly to the net torque, and must be taken into account in order to minimize the counter-torque.
On the other hand, while elimination of counter-torque can be accomplished by any tool or head configuration in which the torques on individual heads or tools are caused to balance out or substantially add to zero, in the case of cleaning heads of tools such as brushes cross-cleaning is most intense when adjacent heads are rotated such that the linear velocities (v) of respective points on relatively moving adjacent edges of the heads have equal magnitudes and opposite directions. This occurs when the "angular velocity" of each pair of adjacent counter-rotating heads has an equal magnitude (angular speed) and opposite direction, with the number of heads (and the width of the layers) determining the number of interfaces at which cross-cleaning effects are most intense.
FIGS. 1-1 and 1-2 illustrate the relationship between "linear speed" and radius in a two layer counter-rotating brush assembly in which the counter-rotating brushes have the same angular speeds, while FIGS. 1-3 and 1-4 illustrate the relationship between "linear speed" and radius in a four layer counter-rotating brush assembly, and FIGS. 1-5 and 1-6 illustrate the relationship in an eight layer assembly. As is apparent from these Figures, the linear speed, which is the relative instantaneous speed between a bristle and the portion of the surface which is being contacted by the bristle, increases linearly across each of the brush heads while at the interface between brush heads, the linear speed of respectively adjacent bristles on the heads is exactly the same but opposite in direction.
Because cross-cleaning occurs between adjacent heads, improved cross-cleaning is obtained with each head added. In addition, as the number of heads increases, and the torque variations across the radii of the heads decreases, the balancing effect also improves, with perfect balance being achieved in theory by an infinite number of heads with infinitesimally small differences in radii across the heads (referred to as the infinitesimal balancing effect). While cost of construction will eventually limit the number of heads, the invention in theory enables cross-cleaning and balancing to be made as close to optimum as desired by increasing the number of heads.
It is known, of course, to provide small appliances such as electric toothbrushes with multiple heads or tools mounted on parallel shafts to rotate in opposite directions. While such appliances are in widespread usage, however, the use of completely separate heads or tools mounted on separate shafts does not optimize the cleaning to any significant degree, but rather simply increases the coverage of the device in order to reduce cleaning time. In contrast, the present invention seeks to split a single tool or head into multiple heads or tools with differential movement not to increase the area cover during one pass of the device, but to provide a variety of performance improvements, including increasing the intensity of the effect provided by the multiple heads in comparison with a conventional rotating or reciprocating device of like area.
While counter-rotating head devices have been proposed for certain specialized applications, such as the spotting brush of U.S. Pat. No. 1,796,641, the counter-rotation taught by the prior art is not such as is necessary to obtain a cross-cleaning effect or to provide a balancing counter-torque (to the contrary, the torque resulting from the spotting action in the '641 patent appears to be de minimus). In addition, although it is known to provide a toothbrush with oscillating counter-rotation as described in U.S. Pat. No. 5,416,942, the prior art fails to recognize the advantages of cross-cleaning by one-way counter-rotation of each head, much less the generalized principles of counter-rotation or side-by-side oscillation discovered by the present inventor which would have made the applicability of the invention to other types of devices evident to the ordinary artisan.
The splitting of a single head or tool into concentric or parallel multiple heads or tools arranged for coaxial rotation or side-by-side oscillation according to the present invention not only solves the above-mentioned problems of conventional devices, but also does so without significantly increasing the complexity of the device, since according to preferred embodiments of the invention, a single drive shaft can be used (although the use of a single drive shaft is not necessary to the invention in its broadest form, since the advantages of easier handling and improved cleaning do not depend on the specific mechanical arrangement used to achieve the differential rotation effect).
The advantage of eliminating counter-torque increases with the power of the device. If one presses a small conventional rotating brush against a surface, there will be a small torque in the direction opposite the direction of rotation, which is countered by the force of the person holding the brush, and which may not even be felt by that person. As power increases, however, a point is eventually reached where it will become impossible to hold the brush. By bifurcating the brush motion into two oppositely rotating sections, the problem of counter-torque will clearly be minimized even for very high power devices which could not ordinarily be handled by the average user. The balancing problem is especially apparent in devices intended to be used on uneven surfaces, such as a car polisher, and also in devices such as floor buffers which have an odd number of heads, and therefore an inherently unbalanced torque.
The cross-cleaning advantage applies even in the case of ordinary linearly reciprocating electric toothbrushes, which one would expect to remove dirt effectively despite the lack of differential motion due to the reversal of motion at the ends of the oscillations. The problem is that either the amplitude of the oscillations is so small that the cleaning tip of the soft bristles will remain relatively stationary even as the brush head moves, or the amplitude will be sufficiently large that the brush head will have moved to another surface before it reverses direction, greatly reducing the cross-cleaning effect provided by the reversal of motion at the end of the oscillations.
While the general concept of providing concentric or parallel multiple heads or tools arranged for coaxial rotation or side-by-side oscillation is believed to be novel and non-obvious, in the intended context of small household appliances, and in particular the cleaning and personal grooming devices described below, those skilled in the art will recognize that the specific mechanical arrangements utilized to achieve the desired differential motion may be in the form of gearing or transmission arrangements which are per se known, although not in the specific context disclosed. The use of bevel gears and planetary or ring/idler gear combinations is of course known and thus the invention in general is not intended to be limited to any such arrangements, although some of the mechanical expedients used to implement the present invention are believed to be especially advantageous in terms of efficiency, reliability, and cost, and thus form a proper basis for one or more claims.